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3rdparty/c-ares-1.18.1/m4/ax_cxx_compile_stdcxx_11.m4 5.23 KB
73ef4ff3   Hu Chunming   提交三方库
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  # ============================================================================
  #  http://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx_11.html
  # ============================================================================
  #
  # SYNOPSIS
  #
  #   AX_CXX_COMPILE_STDCXX_11([ext|noext],[mandatory|optional])
  #
  # DESCRIPTION
  #
  #   Check for baseline language coverage in the compiler for the C++11
  #   standard; if necessary, add switches to CXXFLAGS to enable support.
  #
  #   The first argument, if specified, indicates whether you insist on an
  #   extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
  #   -std=c++11).  If neither is specified, you get whatever works, with
  #   preference for an extended mode.
  #
  #   The second argument, if specified 'mandatory' or if left unspecified,
  #   indicates that baseline C++11 support is required and that the macro
  #   should error out if no mode with that support is found.  If specified
  #   'optional', then configuration proceeds regardless, after defining
  #   HAVE_CXX11 if and only if a supporting mode is found.
  #
  # LICENSE
  #
  #   Copyright (c) 2008 Benjamin Kosnik <bkoz@redhat.com>
  #   Copyright (c) 2012 Zack Weinberg <zackw@panix.com>
  #   Copyright (c) 2013 Roy Stogner <roystgnr@ices.utexas.edu>
  #   Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <sokolov@google.com>
  #
  #   Copying and distribution of this file, with or without modification, are
  #   permitted in any medium without royalty provided the copyright notice
  #   and this notice are preserved. This file is offered as-is, without any
  #   warranty.
  
  #serial 9
  
  m4_define([_AX_CXX_COMPILE_STDCXX_11_testbody], [[
    template <typename T>
      struct check
      {
        static_assert(sizeof(int) <= sizeof(T), "not big enough");
      };
  
      struct Base {
      virtual void f() {}
      };
      struct Child : public Base {
      virtual void f() override {}
      };
  
      typedef check<check<bool>> right_angle_brackets;
  
      int a;
      decltype(a) b;
  
      typedef check<int> check_type;
      check_type c;
      check_type&& cr = static_cast<check_type&&>(c);
  
      auto d = a;
      auto l = [](){};
  
      // http://stackoverflow.com/questions/13728184/template-aliases-and-sfinae
      // Clang 3.1 fails with headers of libstd++ 4.8.3 when using std::function because of this
      namespace test_template_alias_sfinae {
          struct foo {};
  
          template<typename T>
          using member = typename T::member_type;
  
          template<typename T>
          void func(...) {}
  
          template<typename T>
          void func(member<T>*) {}
  
          void test();
  
          void test() {
              func<foo>(0);
          }
      }
  ]])
  
  AC_DEFUN([AX_CXX_COMPILE_STDCXX_11], [dnl
    m4_if([$1], [], [],
          [$1], [ext], [],
          [$1], [noext], [],
          [m4_fatal([invalid argument `$1' to AX_CXX_COMPILE_STDCXX_11])])dnl
    m4_if([$2], [], [ax_cxx_compile_cxx11_required=true],
          [$2], [mandatory], [ax_cxx_compile_cxx11_required=true],
          [$2], [optional], [ax_cxx_compile_cxx11_required=false],
          [m4_fatal([invalid second argument `$2' to AX_CXX_COMPILE_STDCXX_11])])
    AC_LANG_PUSH([C++])dnl
    ac_success=no
    AC_CACHE_CHECK(whether $CXX supports C++11 features by default,
    ax_cv_cxx_compile_cxx11,
    [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
      [ax_cv_cxx_compile_cxx11=yes],
      [ax_cv_cxx_compile_cxx11=no])])
    if test x$ax_cv_cxx_compile_cxx11 = xyes; then
      ac_success=yes
    fi
  
    m4_if([$1], [noext], [], [dnl
    if test x$ac_success = xno; then
      for switch in -std=gnu++11 -std=gnu++0x; do
        cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx11_$switch])
        AC_CACHE_CHECK(whether $CXX supports C++11 features with $switch,
                       $cachevar,
          [ac_save_CXXFLAGS="$CXXFLAGS"
           CXXFLAGS="$CXXFLAGS $switch"
           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
            [eval $cachevar=yes],
            [eval $cachevar=no])
           CXXFLAGS="$ac_save_CXXFLAGS"])
        if eval test x\$$cachevar = xyes; then
          CXXFLAGS="$CXXFLAGS $switch"
          ac_success=yes
          break
        fi
      done
    fi])
  
    m4_if([$1], [ext], [], [dnl
    if test x$ac_success = xno; then
      for switch in -std=c++11 -std=c++0x; do
        cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx11_$switch])
        AC_CACHE_CHECK(whether $CXX supports C++11 features with $switch,
                       $cachevar,
          [ac_save_CXXFLAGS="$CXXFLAGS"
           CXXFLAGS="$CXXFLAGS $switch"
           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
            [eval $cachevar=yes],
            [eval $cachevar=no])
           CXXFLAGS="$ac_save_CXXFLAGS"])
        if eval test x\$$cachevar = xyes; then
          CXXFLAGS="$CXXFLAGS $switch"
          ac_success=yes
          break
        fi
      done
    fi])
    AC_LANG_POP([C++])
    if test x$ax_cxx_compile_cxx11_required = xtrue; then
      if test x$ac_success = xno; then
        AC_MSG_ERROR([*** A compiler with support for C++11 language features is required.])
      fi
    else
      if test x$ac_success = xno; then
        HAVE_CXX11=0
        AC_MSG_NOTICE([No compiler with C++11 support was found])
      else
        HAVE_CXX11=1
        AC_DEFINE(HAVE_CXX11,1,
                  [define if the compiler supports basic C++11 syntax])
      fi
  
      AC_SUBST(HAVE_CXX11)
    fi
  ])